Can we determine the activation energy for ionic conduction from the nuclear- and electron-density distributions?

本课题研究了两种K_2NiF_4型氧化物Pr_2（Ni_0.75Cu_0.25）_0.95Ga_0.05O_4+δ和Pr_2Ni_0.75Cu_0.25O_4 +δ的晶体结构、核密度分布、电子结构和透氧速率。Pr_2（Ni_0.75Cu_0.25）_0.95Ga_0.05O_4+δ和Pr_2Ni_0.75Cu_0.25_O4 +δ在高温下的核密度分布显示了氧离子的-（顶氧O2）-（间隙氧O3）-（顶氧O2）-扩散路径，表明存在间隙扩散机制。发现O2-O3通道上的最小核密度ρN（T）是一个有用的氧扩散系数的微观参数。ρN（T）被认为是扩散瓶颈处的氧概率密度。氧渗透速率ρp（T）随ρN（T）的增大而增大。氧扩散的活化能由log（标准化的氧渗透速率ρP（T）/δ）对T^-1（绝对温度的倒数）的曲线估算，与温度无关，瓶颈处氧原子的形成能由log（ρN（T）/ δ）对T^-1的曲线估算。这些结果表明，间隙氧δ的量与氧化物离子扩散的载流子浓度成正比。

In this project, we have investigated the crystal structure, nuclear-density distribution, electronic structure and oxygen permeation rate of two K_2NiF_4-type oxides of Pr_2(Ni_0.75Cu_0.25)_0.95Ga_0.05O_4+δ and Pr_2Ni_0.75Cu_0.25_O4+δ. Nuclear-density distributions of Pr_2(Ni_0.75Cu_0.25)_0.95Ga_0.05O_4+δ and Pr_2Ni_0.75 Cu_0.25_O4+δ at high temperatures have visualized the -(apical oxygen O2)- (interstitial oxygen O3)-(apical oxygen O2)- diffusional pathway of oxide ions, which indicates an interstitialcy diffusion mechanism. It was found that the minimum nuclear density on the O2-O3 pathway ρN(T) is a useful microscopic parameter for the oxygen diffusivity. The ρN(T) is regarded as the oxygen probability density at the bottleneck for diffusion. The oxygen permeation rate ρp (T) increases with an increase of ρN (T). The activation energy for oxygen diffusion estimated by the plots of log(the normalized oxygen permeation rate ρP (T)/δ ) against T^-1 (reciprocal of absolute temperature) is independent of temperature, as well as the formation energy of oxygen atoms at the bottleneck from the plots of log(ρN(T)/ δ ) against T^-1. These results indicate that the amount of interstitial oxygen δ is proportional to the carrier concentration for the oxide-ion diffusion.